1. Field of the Invention
The present invention relates to a composite high-frequency switch, a high-frequency module, and a communication apparatus. More particularly, the present invention relates to a composite high-frequency switch, a high-frequency module, and a communication apparatus, which is used in a plurality of different communication systems.
2. Description of the Related Art
Presently, in Europe, as a communication apparatus, a dual-band portable phone which operates in a plurality of communication systems, for example, a DCS (Digital Cellular System) in which a 1.8-GHz band is used and a GSM (Global System for Mobile Communications) in which a 900-MHz band is used has been proposed. In contrast to a conventional portable phone which operates in only one communication system, this dual-band portable phone operates in two communication systems. This enables a user to select and to use a suitable communication system.
In the dual-band portable phone, a high-frequency module is operative to switch between a plurality of communication systems and to switch between a transmission circuit and a receiving circuit. A known high-frequency module is disclosed in Japanese Unexamined Patent Application Publication No. 11-168303. This conventional high-frequency module is defined by an antenna switch module which connects the two communication systems DCS and GSM to an antenna, and includes a diplexer and two high-frequency switches. The two high-frequency switches switch between a transmission circuit and a receiving circuit, and include first and second diodes, a transmission line, and an inductor. The anode of a first diode is connected to the antenna terminal side and its cathode is connected to the transmission terminal side, and an inductor is connected between the cathode and a ground. The transmission line is connected between an antenna terminal and a receiving terminal, and the cathode of a second diode is connected to the receiving terminal side and a capacitor is connected between the anode of the second diode and a ground. A control terminal is connected between the second diode and the capacitor.
When this high-frequency module operates, a positive voltage is applied to the control terminal of the high-frequency switch on the selected communication system side, and a zero voltage is applied to the control terminal of the high-frequency switch on the communication system side which is not selected. However, a problem arises in that a received signal or a transmission signal in the selected communication system side leaks to the communication system side which is not selected, and the first and second diodes of the high-frequency switch of the communication system which is not selected are distorted. To solve this problem, a method in which a negative voltage is applied to the control terminal of the high-frequency switch of the communication system side which is not selected, such that a reverse bias is applied to the first and second diodes of the high-frequency switch of the communication system which is not selected.
However, according to the above-described high-frequency module, since a negative voltage must be applied to the control terminal of the high-frequency switch on the communication system side which is not selected, a negative power source must be provided within the dual-band portable phone, which increases the complexity of the configuration of the circuit.
In order to overcome the problems described above, preferred embodiments of the present invention provide a composite high-frequency switch and a high-frequency module which prevents distortion in first and second diodes of a communication system which is not selected without providing a negative power source, and a communication apparatus including the high-frequency module.
A first preferred embodiment of the present invention provides a composite high-frequency switch including a plurality of high-frequency switches, each having a first terminal, a second terminal, a first control terminal, a second control terminal, a first diode, a second diode, and a transmission line, wherein the high-frequency switch is configured such that the first terminal, the transmission line, the first diode, and the second terminal are connected in series, the first terminal side of the transmission line is connected to a ground via the second diode, the first control terminal is connected to the ground side of the second diode, and the second control terminal is connected to the second terminal side of the first diode, and at least two of the plurality of high-frequency switches are configured such that the second control terminals are connected to each other and the connection point thereof is connected to a common control terminal via a resistor.
Another preferred embodiment of the present invention provides a composite high-frequency switch including a plurality of high-frequency switches, each having a first terminal, a second terminal, a first control terminal, a second control terminal, a first diode, a second diode, and a transmission line, wherein the high-frequency switch is configured such that the first terminal, the transmission line, the first diode, and the second terminal are connected in series, the first terminal side of the transmission line is connected to a ground via the second diode, the first control terminal is connected to the ground side of the second diode, the second control terminal is connected to the second terminal side of the first diode, and at least two of the plurality of high-frequency switches are configured such that the first control terminals are connected to each other and the connection point thereof is connected to a common control terminal via a resistor.
Still another preferred embodiment of the present invention provides a composite high-frequency switch including a plurality of high-frequency switches each having a first terminal, a second terminal, a first control terminal, a second control terminal, a first diode, a second diode, and a transmission line, wherein the high-frequency switch is configured such that the first terminal, the transmission line, the first diode, and the second terminal are connected in series, the first terminal side of the transmission line is connected to a ground via the second diode, the first control terminal is connected to the ground side of the second diode, the second control terminal is connected to the second terminal side of the first diode, and at least two of the plurality of high-frequency switches are configured such that the first control terminal of a high-frequency switch and the second control terminal of another high-frequency switch are connected to each other and the connection point thereof is connected to a common control terminal via a resistor.
Preferably, the composite high-frequency switch according to preferred embodiments of the present invention further includes a multilayer substrate having a plurality of sheet layers layered thereon, wherein a diode of the high-frequency switch is mounted on the multilayer substrate, and a transmission line of the high-frequency switch is provided in the multilayer substrate.
Another preferred embodiment of the present invention provides a high-frequency module including a diplexer having an inductor and a capacitor, the diplexer being connected to a connection point of the first diode and the transmission line of the high-frequency switch.
Preferably, the high-frequency module according to preferred embodiments of the present invention further includes a multilayer substrate having a plurality of sheet layers layered thereon, wherein a diode of the high-frequency switch is mounted on the multilayer substrate, and the inductor and the capacitor of the diplexer, and a transmission line of the high-frequency switch is provided in the multilayer substrate.
In the high-frequency module, preferably, a capacitor of the diplexer is connected to the ground, and a grounding electrode of the high-frequency switch is provided between the capacitor and the transmission line of the high-frequency switch.
Another preferred embodiment of the present invention provides a communication apparatus using the composite high-frequency switch according to preferred embodiments described above.
Still another preferred embodiment of the present invention provides a communication apparatus using the high-frequency module according to preferred embodiments of the present invention described above.
According to the composite high-frequency switch of various preferred embodiments of the present invention, by applying a positive voltage to the control terminal of a high-frequency switch in a selected communication system side, a forward bias is applied to the first and second diodes of the high-frequency switch on the selected communication system side, and at the same time, a reverse bias is applied to the first and second diodes of a high-frequency switch on the communication system side which is not selected.
According to the high-frequency module of preferred embodiments of the present invention, since a composite high-frequency switch having greatly improved distortion characteristics is provided, the distortion characteristics of the high-frequency module are also greatly improved.
According to the communication apparatus of preferred embodiments of the present invention, since a composite high-frequency switch or a high-frequency module, having greatly improved distortion characteristics, is provided, the transmission and receiving characteristics of the communication apparatus are greatly improved.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.